There is often a need to administer solid medications in oral liquid forms to patients. These patients include adults who cannot swallow solid dosage forms, infants and children, nonambulatory patients with nasogastric tubes, geriatric patients, and animals. In a typical preparation, a medication available in a tablet or bulk powder form is finely ground, wetted with a wetting agent, and then combined slowly with a liquid vehicle. This technique is flexible and provides a method to treat a patient with a variety of medicaments in alternative dosage forms.
Ideally, a liquid suspending vehicle is thixotropic, has a measurable yield value or is a pseudoplastic power law liquid with a low flow index, is shear thinning, prevents solid particles too large to be suspended from forming a hard cake in the vehicle, is physiologically compatible and results in minimal gastric impact, is resistant to changes induced by the addition of unknown chemical substances, provides a chemically inert environment, and has a pleasant or neutral flavor and mouth-feel (Thompson, J. E., A Practical Guide to Contemporary Pharmacy Practice, Lippincott Williams & Wilkins, Baltimore, Md., 1998, p. 28.1). There are a variety of products currently available whose primary function is to serve as a liquid vehicle for compounding extemporaneous solutions or suspensions. None of the currently available products meet all of the criteria set forth in Thompson (Id.).
Most products currently available employ one or more suspending agents, such as agar, alginic ac, activated attapulgite, bentonite, carbomer, carboxymethycellulose (calcium and sodium salts), carrageenan, microcrystalline cellulose, dextrin, gelatin, guar gum, hydroxypropylmethylcellulose, methylcellulose, pectin, poloxamer, polyoxyethylene oxide, polyvinyl alcohol, povidone, propylene glycol alginate, silicon dioxide, sodium alginate, tragacanth, and xanthan gum (Allen, L. V. Jr., The Art, Science, and Technology of Pharmaceutical Compounding, American Pharmacy Association, Washington, D.C., 1998, p. 169).
While these products are designed to provide permanent suspensions, they suffer from shortcomings including: sedimentation of ingredients added to the suspension; difficulty resuspending sedimented ingredients; hydrolysis of the suspending agent; deactivation, precipitation, or coagulation of the suspending agent due to chemical, electrolyte, or cation sensitivities and/or physical changes such as shear or temperature; and deactivation, precipitation, or coagulation by amphiphilic or detergent-like molecules. In addition, many of the previously formulated liquid suspending vehicles are hyperosmotic, incompatible with one or more frequently compounded medications, and/or have a bulk laxative effect.
Clearly, a substantial need exists for an improved liquid vehicle for preparing medicinal suspensions or solutions.